/Engine/Source/Runtime/Core/Public/Internationalization/TextLocalizationManager.h
Returns a display string with the given namespace and key. If no display string exists, it will be created using the source string or an empty string if no source string is provided. If a display string exists ... ... but it was not localized from the specified source string, the display string will be set to the specified source and returned. ... and it was localized from the specified source string (or none was provided), the display string will be returned.
FTextConstDisplayStringRef GetDisplayString ( const [FTextKey](API\Runtime\Core\Internationalization\FTextKey) & Namespace, const [FTextKey](API\Runtime\Core\Internationalization\FTextKey) & Key, const [FString](API\Runtime\Core\Containers\FString) *const SourceString )